Question: 8 erasers cost $15.04. Which equation would help determine the cost of 4 erasers?
Explanation: There are several equations that could help determine the cost, each with a slightly different approach. Let $x$ represent the unknown cost of 4 erasers. Since 4 erasers cost $x$ , we have the following proportion: $\dfrac{4}{x}$ We can write the fact that 8 erasers cost $15.04 as a proportion: $\dfrac{8}{\$15.04}$ The cost changes along with the number of erasers purchased, and so the two proportions are equivalent. $\dfrac{4}{x} = \dfrac{8}{\$15.04}$